Thread cutting device for double stitch sewing machines

ABSTRACT

A device for simultaneously cutting both the needle thread and the looper thread below a workpiece after the completion of the seam, for use with lockstitch sewing machines. The carrier of an arcuate cutting blade oscillates concentrically about the looper and cooperates with a stationary cutting knife. The driving means and transmitting means for the carrier are arranged on a supporting body provided with lugs. The lugs are inserted and secured in the sewing machine. This device can be additionally installed in existing sewing machines without any special provisions.

United States Patent Landwehr 1 Sept. 4, 1973 [54] THREAD CUTTING DEVICE FOR DOUBLE 3,141,432 7/1964 Reeber et a1. 112 252 CH SEWING MACHINES 3,173,392 3/1965 Hedegaard..... 112/252 3,173,393 3/1965 Adam 112/252 [75] Inventor: Gunter Landwehr, Sennestadt,

Germany Primary ExaminerWerner H. Schroeder [73] Assignee: Koch Adler AG, Bilefeld, Germany A rney-Jacob L. Kollin [22] Filed: Dec. 15, 1971 [21] [57] ABSTRACT Appl. No.: 208,363

A device for simultaneously cutting both the needle thread and the looper thread below a workpiece after the completion of the seam, for use with lockstitch sewing machines. The carrier of an arcuate cutting blade oscillates concentrically about the looper and cooperates with a stationary cutting knife. The driving means and transmitting means for the carrier are arranged on a supporting body provided with lugs. The lugs are inserted and secured in the sewing machine. This device can be additionally installed in existing sewing machines without any special provisions.

4 Claims, 7 Drawing Figures I 30] Foreign Application Priority Data Dec. 17, 1971 Germany P 20 62 201.9

[52] U.S. C1. 112/252 [51] Int. Cl D051) 65/02 [58] Field of Search 112/252 [56] References Cited UNITED STATES PATENTS 3,443,540 5/1969 Hannemann et a1 112/252 PATENTEDSEP 4:915

SHEET 1 0F 4 vui PATENTEDSEP 4191a SHEET 2 BF 4 BACKGROUND OF THE INVENTION This invention relates to a thread cutting device for a conventional lockstitch sewing machine, and more particularly to a thread cutting device, in which the needle thread and the looper thread are simultaneously cut by an arcuate cutting blade, which .is mounted for oscillation concentrically about the looper, and a stationary cutting blade.

It is an object of the present invention to provide a thread cutting device for cutting off both the needle thread and the bobbin thread below the throat plate after finishing a sewing operation, so that the residue thread ends will have a short length.

It is a further object of the invention to provide an improved cutting device for sewing machines of the above type, which is both simple in construction, and

' reliable in operation, and which can be attached to or disassembled from a sewing machine as a nearly complete unit.

It is another object of the invention to provide a thread cutting device, which will have a small number of mechanical parts.

It is a further object of the invention to provide simple means for controlling the loosening of the needle thread tension required before the operation of the thread cutting device.

There are already known thread cutting devices in lockstitch sewing machines. In one of such devices the carrier arranged coaxially in relation to the looper and receiving the thread catcher, is in releasable driving connection with the looper shaft, while a coupling disk is secured to a drive shaft for the thread cutting device, the drive shaft extending parallel to the looper shaft. The coupling disk is provided with a spring loaded follower arm pivoted about a pin arranged parallel with the drive shaft. The follower arm projects into the path of motion of a pin projecting laterally from a gear, which is mounted on the drive shaft and in driving connection with the looper shaft. Due to the proportionally high mechanical expenditure for driving and controlling the thread catcher, this device, disclosed in U.S. Pat. No. 3, 173, 392 does not appear to be adapted for the subsequent installation in already existing sewing machines.

In a known thread cutting device of the mentioned type, in which the thread catcher is also coaxially arranged in relation to the looper and disposed on a rotatable carrier, the thread catcher actuated by means of the starting and stopping device of the sewing machine and driven by means of an electromagnet, which is secured to the table of the sewing machine, engages the threads to be cut off during its first moving phase, in order to carry the same to the stationary cutting blade, while for the return stroke into its initial position there is provided a relatively strong restoring spring. However, for this thread cutting device having only a few mechanical elements and suitable to be installed to already existing sewing machines with only a few technical resources a relatively strong electromagnet of a larger dimension is required. The electromagnet must not only apply the required force for cutting off the threads but also to provide the tension of the restoring spring for the thread catcher. This cutting device is described in U.S. Pat. No. 3, 443, 540.

It is the purpose of the present invention to provide a thread cutting device for lockstitch sewing machines having a looper rotating about a horizontal axis for cutting off simultaneously the needle thread and the looper thread below the throat plate by means of an annular blade, which is coaxially arranged in relation to the looper and rotatably driven by a comparatively small electromagnet controlled by the starting and stopping means of the sewing machine and arranged on the bedplate of the sewing machine, said thread cutting device requiring only a small number of mechanical elements and adaptable for using in already existing sewing machines without substantial manipulations.

SUMMARY The armature of the electromagnet carries an extension member provided with a fork engaging a crankpin, which is secured to the toothed segment. The ringshaped carrier for the arcuate blade, the toothed segment and the electromagnet are received by a support ing body formed with lugs, which are received in the bores in the bedplate. The carrier is received in a bayonet catch and pivoted in a recess of the supporting body. I

There is further provided a device for releasing .the needle thread tension, which comprises a lever pivotally attached to the supporting body, a roller pivotally attached to the lever, a spring for pressing the roller against a guiding edge of the toothed segment, a traction rope fastened to the lever, a tube for receiving and leading the traction rope to the thread tension, and means connected with the free end of the traction rope, for actuating the operating pin of the thread tension. The means for actuating the operating pin consist of a cylindrical cam member provided with a conical part and fastened to the free end of the traction rope, a double armed lever actuated by the cylindrical cam member and transmitting the movements to the operating pin of the thread tension, and a restoring pin for drawing back the cam member out of the radius of action of the double armed lever.

BRIEF DESCRIPTION OF THE DRAWINGS the thread cutting device;

FIG. 6'is a section taken along line IVI VI of FIG. 1, on an enlarged scale and FIG. 7 is a section taken along line VIIVII of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, FIG. 1 and 2 show a sewing machine 1 having a conventional bedplate 2, with a standard 3 secured to the latter and formed with an overhanging arm 4 terminating in a head 5. In the overhanging arm 4 is supported an arm shaft 6, which drives a needle bar 7, reciprocating up and down in the head 5 and carrying a needle 8. Secured to the arm shaft 6 is a toothed belt pulley 9 driving a looper drive shaft 12 pivoted in the bedplate 2, by means of a toothed belt 10 and a toothed belt pulley 11. The looper drive shaft 12 drives, by means of gear wheels 13, 14 (FIGS. 3 and 4) and with a double number of revolutions, a looper shaft 15 carrying a cylindrically rotatable looper 16, which cooperates with the needle 8.

The sewing machine 1 is provided with a feed dog 17 (FIGS. 2 to 4) carried by a feed dog bar 18, to which are imparted, in known manner, reciprocating longitudinal movements by means of a driven shaft 19 (FIG. 2) and lifting movements derived from the looper drive shaft 12.

Driving of the sewing machine 1 (FIG. 1) is effected by means of a stop motor 20 via a V-belt 21 to the arm shaft 6 carrying a positioning device 20', which cooperates with the motor 20. The motor 20 causes the needle 8 to be stopped in the lower dead position and subsequently to be moved at a low speed into its upper dead position.

A supporting body 22 (FIGS. 2 to 5) is provided with lugs 23, displaceably and clampably received by means of screws 24 in bores 25 located in the bedplate 2. As may be seen in FIG. 5, the supporting body 22 is formed with an essentially circular recess 26 with laterally arranged cutouts 27 for receiving a ring-shaped carrier 28 for an arcuate blade 29. The carrier 28 with its cylindrical part 28' is supported in the recess 26 of the supporting body 22. When inserting the carrier 28 into the recess 26, two side walls 30 are guided like a bayonet catch through the cutouts 27 and serve for the purpose of preventing the ringshaped carrier 28 from axial displacement. The carrier 28 is also provided on a section of its circumference with a toothed part 31 meshing with the teeth 32 of a toothed segment 33, which is pivoted about a bolt 35 to the supporting body 22 by means of roller bearings 34 (FIGS. 3 and 5). Between the toothed segment 33 and a parallel extending plate 36 associated with the latter, is arranged a cam follower in the form of a roller 38 (FIGS. 2 and 5) rotatable about a bolt 37 and resting against a cam disk 39 secured to the looper drive shaft 12.

The supporting body 22 has angular tongues 40, to which is secured, by means of screws 42, an electromagnet 41, the armature 43 of which is provided with an extension member 44. The latter is formed at its end with a fork 45 engaging a crank pin 46 arranged between the plate 36 and the toothed segment 33.

Pivoted about a bolt 48 a lever 47 carrying a roller 49, which is under the tension of a spring 50 arranged between the lever 47 and the bedplate 2, against a guiding edge 51 of the toothed segment 33.

A traction rope 52 is secured to the free end of the lever 47 is secured guided through a tube 53 into the head 5 of the sewing machine 1 (FIG. 1). The end of the traction rope 52 (FIGS. 6 and 7) is secured by means of a screw 54 in a cylindrical cam member 55, the shank 56 of which is guided in a tube 57. At its end, the shank 56 is provided with a conical part 58, which cooperates with the arm 59 of a double armed lever 60, while the other arm 61 (FIG. 7) of the latter abuts against the operating pin 62 for releasing the thread tension disks 63 of the thread tension device 64. The tube 57, provided with a recess 65 for engaging the arm 59, is secured in a block 66 and received with its one end in a bore 68 located in a wall 67 at the end of the overhanging arm 4. Between the head 69 of the cylindrical cam member 55 and the block 66 is provided a restoring spring 70. The double armed lever 60 is pivoted about a shank 71 of a thread bolt 72, screwed in the wall 67 and serving to fix the block 66 to the wall 67, while using a distance ring 73.

The arcuate blade 29 cooperating with a stationary cutting knife 74 (FIGS. 2, 3 and 5) has a point 75, in order to be adaptable to enter the needle thread loop during the forward motion of the arcuate blade 29, and an engaging edge 76 for engaging the looper thread extending to the workpiece as well as the shank of the needle thread loop leading to the workpiece, and a cutting edge 77 cooperating with the stationary cutting knife 74 for simultaneously cutting off the engaged threads during the back stroke of the arcuate blade 29.

During the operation of the sewing machine, the cam follower 38 of the toothed segment 33 (FIG. 2) is held out of contact with the cam disk 39 by means of a (not shown) pressure spring located in the electromagnet 41.

On energizing the electromagnet 41, changing over the electrical switching mechanism of the stop motor 20 to a slow motor speed, the armature 43 is attracted, thus pressing the cam follower 38 against the cam disk 39, which is formed in such a manner, that the toothed segment 33 and thus also the ring-shaped carrier 28 with the associated arcuate blade 29, are only moved out of their starting positions (FIG. 2) if the needle 8 is not in the area of the stitch hole. After the point of the arcuate blade 29 has entered the needle thread loop, the arcuate blade 29 is returned into its starting position as a result of the rotation of the cam disk 39, while the electromagnet 41 is still energized. The arcuate blade 29 carries the engaged threads to the stationary cutting knife 74 to be cut off. During the forward motion of the arcuate blade 29, also the shank 56 positioned by means of the guiding edge 51 (FIGS. 2, 6, 7) on the toothed segment 33 and the spring 50 via the traction rope 52, is drawn into the tube 57 against the tension of the restoring spring 70, which is weaker in comparison with the spring 50, so that the conical part 58 rests against the arm 59 of the double armed lever 60, thus separating the thread tension disks 63 from each other by means of the operating pin 62. Thus, at the return stroke of the arcuate blade 29, a sufficient length of needle thread is drawn off from the needle thread supply through the needle eye for forming an initial stitch.

What I claim is:

1. In combination with a lockstitch sewing machine having stitch forming elements including a reciprocating needle driven by an arm shaft, a looper driving shaft in driven connection with said arm shaft, a cylindrical rotatable looper driven by said looper driving shaft and provided with a needle thread seizing beak, a bed plate, a throat plate arranged above said looper within said bed plate, a thread tension element for the needle thread and a thread tension release for said thread tension element, thread cutting means for the needle thread and the looper thread comprising an arcuate blade, a carrier pivoted about said looper for concentric oscillation about said looper and carrying said arcuate blade, said carrier being provided with a toothed part, a stationary cutting knife engageable by said arcuate blade to sever said looper and needle threads when said needle is in an upper position, a toothed segment meshing with said toothed part of said carrier and having a cam follower and a crank pin, a cam disk in driving connection with said looper shaft and coacting with said cam follwer, an electromagnet having an armature, an extension member, carried by said armature and being formed with a fork, for cooperating with said crankpin, and a supporting body for carrying said electro magnet, said toothed segment and said carrier for said arcuate blade, and provided with lugs receivable in said sewing machine.

2. In the combination as claimed in claim 1, wherein said carrier is formed with a cylindrical part and two sidewall parts at the end of said cylindrical part, and said supporting body is provided with a circular recess for pivotally receiving said cylindrical part of said carrier and two cutouts for the passage of said two side wall parts during the inserting of said carrier into the recess of said supporting body in a bayonet joint-like manner.

3. In the combination as claimed in claim 1, wherein said thread tension comprises two thread tension disks, spring means for pressing said disks together and an operating pin bearing upon one of said disks, for detaching said one disk from the other, and said thread tension release includes said toothed segment provided with a guiding edge, a lever pivotally attached to said supporting body, a roller pivotally attached to said lever, a spring for pressing said roller on said guiding edge of said toothed segment, a traction rope secured to said lever, a tube for receiving and leading said traction rope to said thread tension, and means connected with the free end of said traction rope, for actuating said operating pin of said thread tension.

4. In the combination as claimed in claim 3, wherein said means for actuating said operating pin of said thread tension comprises a cylindrical cam member secured to said free end of said traction rope and provided with a conical part, a double armed lever, one arm of which cooperating with said conical part of said cylindrical cam and the other arm bearing upon said operating pin of said thread tension when said one arm has been actuated by said cylindrical cam member, and a restoring spring acting upon said traction rope for drawing back said cam member from said one arm of said double armed lever when said sewing machine is in the operative position. 

1. In combination with a lockstitch sewing machine having stitch forming elements including a reciprocating needle driven by an arm shaft, a looper driving shaft in driven connection with said arm shaft, a cylindrical rotatable looper driven by said looper driving shaft and provided with a needle thread seizing beak, a bed plate, a throat plate arranged above said looper within said bed plate, a thread tension element for the needle thread and a thread tension release for said thread tension element, thread cutting means for the needle thread and the looper thread comprising an arcuate blade, a carrier pivoted about said looper for concentric oscillation about said looper and carrying said arcuate blade, said carrier being provided with a toothed part, a stationary cutting knife engageable by said arcuate blade to sever said looper and needle threads when said needle is in an upper position, a toothed segment meshing with said toothed part of said carrier and having a cam follower and a crank pin, a cam disk in driving connection with said looper shaft and coacting with said cam follwer, an electromagnet having an armature, an extension member, carried by said armature and being formed with a fork, for cooperating with said crankpin, and a supporting body for carrying said electro magnet, said toothed segment and said carrier for said arcuate blade, and provided with lugs receivable in said sewing machine.
 2. In the combination as claimed in claim 1, wherein said carrier is formed with a cylindrical part and two sidewall parts at the end of said cylindrical part, and said supporting body is provided with a circular recess for pivotally receiving said cylindrical part of said carrier and two cutouts for the passage of said two side wall parts during the inserting of said carrier into the recess of said supporting body in a bayonet joint-like manner.
 3. In the combination as claimed in claim 1, wherein said thread tension comprises two thrEad tension disks, spring means for pressing said disks together and an operating pin bearing upon one of said disks, for detaching said one disk from the other, and said thread tension release includes said toothed segment provided with a guiding edge, a lever pivotally attached to said supporting body, a roller pivotally attached to said lever, a spring for pressing said roller on said guiding edge of said toothed segment, a traction rope secured to said lever, a tube for receiving and leading said traction rope to said thread tension, and means connected with the free end of said traction rope, for actuating said operating pin of said thread tension.
 4. In the combination as claimed in claim 3, wherein said means for actuating said operating pin of said thread tension comprises a cylindrical cam member secured to said free end of said traction rope and provided with a conical part, a double armed lever, one arm of which cooperating with said conical part of said cylindrical cam and the other arm bearing upon said operating pin of said thread tension when said one arm has been actuated by said cylindrical cam member, and a restoring spring acting upon said traction rope for drawing back said cam member from said one arm of said double armed lever when said sewing machine is in the operative position. 